Condensation barrier for a coop

Hi,
I am designing a chicken coop and came across the info that humidity can condense under the roof top at night in winter and a way to avoid this condensation to occur is to attach a condensation barrier just under the roof.
The type of materials that I have seen used lately are of this type: does anybody know of any alternative, more sustainable, materials that can be used instead?
Cheers

Hi Antonio, yes condensation can easily form on metal roofing when it's exposed to the interior of the building.  I believe there are at least two ways to prevent it.

1.  Catch the drops and let them run off the roof assembly.  I think this is done when putting metal roof on a house.  First you put on a wooden roof deck, then put a layer of tar paper or roof membrane, then the metal.  This has the side effect of addressing #2 below...

2.  Keep the underside of the metal from being exposed to humid warmer air.  May or may not be possible in a coop.  With enough ventilation on the underside of the metal, it may be able to stay condensation free.  

Basically, if the roof metal is 20 degrees C, and the dew point of the air outside the coop is 21C, that air won't condense.  But if the dew point inside the coop is 19C (either due to higher humidity or warmer air holding a bit more water), it will condense on the slightly cooler roofing.

Edit:  I see I didn't really answer your question...  Any material that keeps the air of the coop from touching the metal should do the trick.  It would help if it didn't rot when it get a drop or two on it.  Not sure what that material may be.

There are many condensation barriers on the market.  While I do not have a metal roof , I did have a friend who had a simple pitched roof on his coop.  The design was such that the water would run along the metal to the outside of the coop.  He claimed it worked.